The need for developing large clamping forces in connectors for securing two members together has long been recognized. Providing large clamping forces is especially important when the connector is to be used for connecting two tubular members of an underwater well installation, since the connection must then withstand not only large forces resulting from component weight and the actions of waves and currents but also large internal fluid pressures. All of the successful prior-art connectors employed in the underwater well field for developing high clamping forces appear to employ annular locking means, varying from annularly arranged locking dogs to a single split locking ring, the locking means being carried by one of the members to be connected and having a frustoconical locking shoulder to engage with a mating shoulder carried by the other member. Opposed transverse end surfaces are provided, and the effect of the locking means, when actuated, is to clamp the end faces together, the locking shoulders providing a strong wedging action to generate the clamping force. In such connectors, actuation of the locking means is accomplished by rectilinear power devices which act in a direction generally axially of the connector. To convert the action of the power devices into effective movement of the locking means, it has become a standard practice to have the power device force a driving ring axially relative to the connector, the driving ring having a frustoconical camming face which slidably engages the locking means to force the locking means generally radially and thus cause the desired wedging action at the locking shoulders. Connectors of this general type are described, for example, in the following U.S. Patents:
U.S. Pat. No. 2,962,096, Knox PA0 U.S. Pat. No. 3,096,999, Ahlstone et al PA0 U.S. Pat. No. 3,228,715, Neilon et al PA0 U.S. Pat. No. 4,200,312, Watkins.
Particularly in the case of underwater well connectors, the difficulties encountered in achieving satisfactory connections are increasingly severe. Such connectors have always been required to withstand both large internal fluid pressures and great, frequently transient, external forces. However, with installations of wells occurring at ever-increasing water depths, and with wells exhibiting increasing large internal pressures, the forces tending to make the connection fail continue to increase. Thus, underwater wellheads are now being required to withstand and seal against internal pressures as high, e.g., as 15,000 p.s.i., and water depths for such installations are now likely to be measured in thousands of feet, so that forces applied to the connector via, e.g., a riser are correspondingly larger. Prospective users of such connectors therefore present increasingly severe specifications for the connector, and the requirements of such specifications prove difficult to meet, so there is an increasing need for improvement of connectors of this general type.
It has been recognized that, in such connectors, it is desirable to place the mating surfaces of the two members to be connected under a large compressive preload, advantageously just short of the yield point of the metal. The preload is established by first engaging the frustoconical locking shoulders and then continuing to supply a large actuating force to the locking means to create a very strong wedging action between the locking shoulders. Success of this action is limited by the adverse effect of sliding friction under the great pressures required, and the desired large compressive preload has frequently not been achieved in practice despite the use of large actuating motors. As disclosed in aforementioned application Ser. No. 327,449, a remarkable improvement in the efficiency of such connectors can be achieved by employing rolling antifriction elements between the camming surface of the driving ring and the cam follower surface of the locking means. However, provision of connectors including the antifriction elements has been difficult to achieve in commercially acceptable form.